text: Magic angle spinning (MAS) is a technique routinely used in solid-state NMR to produce narrower NMR and more intense NMR lines. This is achieved by rotating the sample at the magic angle θ (ca. 54.74°, where cosθ=1/3) with respect to the direction of the magnetic field, which has the effect to cancel, at least partially, anisotropic nuclear interactions such as dipolar, chemical shift anisotropy, and quadrupolar interactions. To achieve the complete averaging of these interactions, the sample needs to be spun at a rate that is at least higher than the largest anisotropy.
  Spinning a powder sample at a slower rate than the largest component of the chemical shift anisotropy results in an incomplete averaging of the interaction, and produces a set of spinning sidebands in addition to the isotropic line, centred at the isotropic chemical shift. Spinning sidebands are sharp lines separated from the isotropic frequency by a multiple of the spinning rate. Although spinning sidebands can be used to measure anisotropic interactions, they are often undesirable and removed by spinning the sample faster or by recording the data points synchronously with the rotor period.